1. Field of the Invention
The present invention relates generally to variable geometry turbine control systems, and more particularly to variable geometry turbocharger (VGT) systems and control thereof for use in internal combustion engines, and especially heavy duty diesel engines.
2. Background and Prior Art
Turbochargers are conventionally used in internal combustion engines to increase the amount of injected intake air so as to increase the output of the engine. In general, the turbocharger consists of a turbine wheel mounted in the exhaust manifold of the engine and a compressor coupled to the turbine wheel and mounted in the intake manifold of the engine. As exhaust gases flow past the turbine wheel it is rotated, causing the compressor to also rotate which increases the pressure of the intake air being charged into the engine cylinders, mixing with fuel and thereafter undergoing combustion.
A known objective with turbocharger design is the attainment of efficient operation over the entire rpm range of the engine. For example, if a turbocharger is designed to provide maximum torque at low engine speeds, at high engine speeds the turbine wheel will rotate at an excessive speed, eventually causing damage by supplying too much air to the engine, and causing excessive wear of the turbocharger parts. On the other hand, if a turbocharger is provided to operate most efficiently at high engine speeds, the efficiency of the turbocharger will be undesirably low when the engine is running at low speeds.
Variable geometry turbochargers or VGTs are usually provided with control of the configuration of the turbine scroll or throat to vary the velocity of exhaust gases flowing past the turbine wheel, or control of the turbine vane angle to vary the amount of exhaust gases "caught" by the turbine. Thus, by suitably changing the turbine configuration according to the engine operating state, more efficient turbocharger operation can be realized over a wider rpm range.
Various control regimes for VGTs are known in the art. See, U.S. Pat. Nos. 4,756,161, 4,769,994, 4,660,382, and 4,741,163. Such systems typically adjust VGT geometry based on engine speed or engine load (fuel quantity), or on supercharging pressure.
However, there remains a need for improvement in optimizing control of VGT configurations taking into account engine operational states, to achieve even higher efficiencies of operation.